Development and application of ultra-precision machining technology

Abstract : Ultra-Precision Machining technology, as a manufacturing method of micro-optical components, has many advantages that other conventional methods do not have. This paper reviews the development of ultra-precision machining technology and looks forward to its potential application in the processing of micro-optical components.

Key words : ultra-precision machining; micro-optics

1 Micro-optical overview

1.1 Definition and name

Micro-optics is an emerging science that belongs to the cross-disciplinary field of many frontier disciplines. With the latest research results of microelectronics industry technology, micro-optics is one of the most advanced research directions in the world and has a wide application prospect. Micro-optical components (MOC) are free-optical curved surfaces and microstructured optical components with surface-accuracy up to sub-micron dimensions and surface roughness up to nanometers. The free optical surface includes a rotating aspheric surface with a rotary axis (such as a paraboloid, an involute surface, etc.), and a non-rotating aspheric surface without any axis of symmetry, such as a Zernike aberration equation surface. Microstructures refer to microsurface topological shapes with specific functions, such as grooves, microlens arrays, etc., as shown in Figure 1 (Figure 1 omitted) of the micropyramid structure surface. These structures determine the reflection, transmission or diffraction properties of the light, allowing the optical designer to optimize the optical system, reduce weight and reduce volume. Typical micro-optical components such as holographic lenses, diffractive optical elements (DOE) and gradient-index lenses, etc., can be used in a variety of optoelectronic instruments to make optoelectronic instruments and their components more compact, array and integrated. Turn.

1.2 Application of micro-optical components

Micro-optical components are key components in the manufacture of small-scale optoelectronic subsystems. They have the advantages of small size, light weight, low cost, and the ability to implement new functions such as micro, array, integration, imaging, and wavefront conversion that are difficult to achieve with common optical components. As the miniaturization of the system continues to become a trend, it is used in almost all engineering applications, both in the field of modern defense science and technology, and in the general industrial field. On the military side, military photoelectric systems developed and produced by Western countries after the 1970s, such as military laser devices, thermal imaging devices, low-light night vision helmets, infrared scanning devices, missile guides, and various zoom lenses, have been used to varying degrees. Aspherical optical parts are used. In the general civil photovoltaic system, free aspherical parts can be applied to a variety of optoelectronic imaging systems. Such as the display system that provides flight information in the aircraft; the viewfinder and zoom lens of the camera; the 锗 lens in the infrared wide-angle horizon; the microscope objective read-out head for recording and recording; the indirect ophthalmoscope for medical diagnosis, the endoscope, progressive Lens and the like. Microstructured optical components are used in a wide variety of applications, such as microslot structures in fiber optic connectors, microlens arrays for liquid crystal displays, F-theta lenses for laser scanning, beam splitters for laser heads, etc. It is used in many of the products we use every day, such as mobile phones, PDAs, CDs and DVDs.

1.3 Micro-optical component processing method

Driven by application requirements, research on micro-optical component processing technology is also deepening, and a variety of modern processing technologies have emerged, such as electron beam writing technology, laser beam writing technology, lithography technology, etching technology, LIGA technology, and replication. Technology and coating technology, among which the most mature technologies are etching technology and LIGA technology. These technologies are basically developed from the micro-machining technology of microelectronic components, but unlike electronic components, three-dimensional molding accuracy and assembly accuracy are critical to optical components and will directly affect their performance, so these Each method has its own flaws and limitations of use. For example, due to the limitation of the depth of field of view, lithography is limited to the processing of two-microstructures and small aspect ratio three-dimensional structures. Sacrificial layer etching technology can achieve quasi-three-dimensional processing, but it is easy to cause internal stress and affect the final Mechanical performance, and equipment cost is very expensive; the high-collimation X-ray source used by LIGA technology is generally obtained by synchrotron radiation accelerator, and the cost is much higher than that of lithography equipment. It is difficult for general laboratories and enterprises to bear. Electron beam writing technology can process nano-scale precision structures, but it is inefficient and difficult to mass produce. Reproduction techniques, including thermoforming, compression molding, and injection molding, are low-cost technologies suitable for mass production, but require high precision and durability.

Another method of processing micro-optical components is ultra-precision machining. Recently, "Fortune" magazine has the following sentence: "Ultra-precision machining technology acts on optical components as if the integrated circuit had an effect on electronic components." Although this sentence is not exaggerated, it shows that the processing of micro-optical components with ultra-precision machining technology has attracted great attention. The application of ultra-precision machining technology in the processing of micro-optical components will be discussed in detail in the next section.

2 Application of ultra-precision machining technology in the processing of micro-optical components

Ultra-precision machining techniques use tools to change the shape of a material or to destroy the surface of a material to achieve the desired shape in a cut form. Such as single crystal diamond turning and milling, grinding, fast cutting and mechanical polishing. This section focuses on ultra-precision machining techniques for machining optical components and their molds.

2.1 Development of key technologies for ultra-precision machine tools

The development of computer-aided design technology, especially finite element analysis technology, provides a convenient means for optimizing the overall structure of ultra-precision machine tools, which makes the rigidity and stability of machine tools continuously improve. At present, the typical structure of a single crystal diamond lathe has a "T" type layout structure, the main shaft is generally mounted on the X-direction rail, and the cutter is mounted on the Z-direction rail. In the past ten years, with the rapid development of computer technology, some key technologies of ultra-precision machine tools, such as control technology, feedback system, servo drive, etc., have made great progress, improving the machining accuracy of ultra-precision machine tools. At present, ultra-precision has been able to directly process surfaces with a roughness of 1 nm. The development of these key technologies is summarized as follows: the use of natural granite as the machine bed, which has very high thermal stability and mechanical stability; the use of air spring system for vibration isolation; the use of liquid or gas static pressure rails, so that Increased damping, smooth motion, no friction; DC linear motor fast drive system, with good dynamic stiffness; high-speed air spindle, high load capacity, high stiffness, can improve machining accuracy; open computer numerical control technology (CNC), easy Application of third-party control software to improve machining accuracy; high-resolution detection device can provide accurate position feedback; use of fast servo mechanism to realize multi-axis system macro-micro-combination technology for processing complex profiles; online measurement and error compensation Technology, correctly measuring workpiece residual errors and ultimately eliminating errors.

2.2 Application examples

The development of electronic technology and optical technology has greatly promoted the application of free aspherical and other non-conventional geometric micro-structured optical components. The emergence of some optical design software makes it easy for optical designers to optimize the performance of optical systems, but it also complicates optical components, which requires micro-optical component manufacturing technology to process these complex optical components. . For micro-optical component designers and manufacturers, single-crystal diamond ultra-precision machining technology has many advantages, such as the ability to process true three-dimensional structures; the forming accuracy of the machined parts is sub-micron; the surface roughness reaches Ra value of 5 nm. Some materials can even reach 1nm; they can process structures with large aspect ratios. Therefore, in the past ten years, the application examples of ultra-precision machining technology in the processing of micro-optical components are gradually increasing. Such as single crystal diamond ultra-precision processing technology has been successfully applied to the processing of contact lenses, prisms, aspherical lenses, microlens arrays, pyramid microstructure surfaces, anti-reflective gratings and other structures. Figure 2 shows the microstructure of a single crystal diamond lathe (Figure 2 is omitted). Although ultra-precision machining technology has many advantages for the processing of some structural optical components, combining ultra-precision machining technology with replication molding technology may be the most effective way to process micro-optical components, that is, using ultra-precision machining technology to process replica molds. Then, the mold is used to fabricate a micro-optical element. To process optical component molds with single crystal diamond lathes, it is necessary to select appropriate processing parameters to reduce burrs, reduce mold errors, and to machine suitable diamond tools. Fresnel lenses made with diamond lathes have been used in overhead projectors for great success, as shown in Figure 3 (Figure 3).

3 Summary

The continuous development of micro-optics technology puts forward higher requirements for micro-optical component manufacturing technology. Ultra-precision machining technology has developed rapidly in the past decade and has many traditional optical manufacturing technologies, such as lithography and LIGA technology. Advantages such as: 1 can process the real three-dimensional structure, and the accuracy is up to nanometer level; 2 can process the floating alignment structure on the mold; 3 can process different aspect ratio structures on the same component. In the field of micro-optics manufacturing, many similar products are processed by many different methods, which illustrates the immaturity of micro-optical manufacturing technology, although the application of ultra-precision machining technology in micro-optical components and their mold processing has A lot of advantages, but still in the initial stage of development. Therefore, ultra-precision machining technology has great potential for development. We believe that the combination of ultra-precision machining technology and replication molding technology will definitely promote the development of micro-optics and its integration technology.